Apparatus and method for spinal stablization

ABSTRACT

A surgical method and apparatus for implanting a spinal fusion implant includes a rigid centering guide having a distal end sized to be inserted into the disc space with the guide extending along a longitudinal axis from a distal end to a proximal end. The guide includes a first external guide surface which extends at least partially between the distal end and the proximal end. The external guide surface is shaped complimentary to an external guided surface of a drill guide. The external guide surface and the guided surface are nested such that the guided surface slides against the external guide surface along a path of travel parallel to the longitudinal axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 08/921,001, filed Aug. 29, 1997 (now U.S. Pat. No. 6,086,595, issuedJul. 11, 2000), which application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to spinal stabilization surgical procedures andapparatus for performing such procedures. More particularly, thisinvention pertains to an apparatus and method for implanting a fusionspinal implant between two vertebrae.

2. Description of the Prior Art

Chronic back problems cause pain and disability for a large segment ofthe population. In many cases, chronic back problems are attributed torelative movement between vertebrae in the spine.

Orthopedic surgery includes procedures to stabilize vertebrae. Commonstabilization techniques include fusing the vertebrae together.

Recently, spinal implants have been developed to facilitate successfulfusion of vertebrae. In such procedures, a bore is formed betweenopposing vertebrae to be fused. An implant, commonly containing bonegrowth-inducing material such as harvested bone chips, is placed withinthe bore.

In order to enhance the successful procedure, a bore should be formedcentrally between the vertebrae such that the bore cuts equally intoboth vertebrae. Also, from time to time, it is desirable to place twoimplants within the same disc space. In such procedures, it is desirablethat the vertebrae be spaced apart by a minimum spacing sufficient toprevent the implants from contacting one another during the implantingprocedure. In the prior art, numerous methods have been disclosed forperforming spinal stabilization procedures.

A spinal implant and stabilization procedure is taught in U.S. Pat. Nos.5,015,247 and 5,484,437 both to Michaelson, dated May 14, 1991 and Jan.16, 1996, respectively. That patent teaches a threaded spinal implant aswell as a method of implantation including certain tools to form a boreinto which the implant is threaded. An implant and surgical method arealso shown in U.S. Pat. No. 4,961,740 to Ray, et al., dated Oct. 9,1990, as well as U.S. Pat. No. 5,026,373 to Ray, et al., dated Jun. 25,1991. The latter patent teaches preparing a bore for the implant bydrilling over a pilot rod.

In addition to cylindrical threaded implants such as those shown in U.S.Pat. No. 5,015,247, implants may take on different geometries, includingnon-cylindrical implants such as those shown in U.S. Pat. No. 5,609,636dated Mar. 11, 1997. Also, conical implants have been suggested, wherethe conical implants have a conical angle approximating a desirablelordosis between the opposing vertebrae.

In surgical procedures involving implants, it is desirable that thesurgical procedure be performed accurately to ensure central positioningof the implant within the disc space between the opposing vertebrae.U.S. Pat. No. 5,489,307 to Kuslich, et al., dated Feb. 6, 1996, teachesa plurality of instruments and a surgical method for preparing a borefor receiving an implant. That procedure results in accuratelypositioning an implant centrally between the opposing vertebrae whileavoiding certain disadvantages with other prior art techniques asdiscussed more fully in the '307 patent. Unfortunately, the method andprocedure of the '307 patent requires a large number of instrumentswhich must be accurately selected and manipulated throughout theprocedure. It is an object of the present invention to provide anapparatus and method for performing spinal stabilization using a reducednumber of instruments in order to simplify the procedure withoutsacrificing the accuracy achieved with the procedure of the '307 patent.Furthermore, it is an object of the present invention to provide asurgical procedure that can be performed posteriorly, anteriorly,laterally, or as a laparoscopic procedure.

SUMMARY OF THE INVENTION

According to the preferred embodiment of the present invention, anapparatus and method are disclosed for implanting a spinal fusionimplant into a disc space separating a first vertebra and a secondvertebra. The method comprises inserting a distal end of a rigidcentering guide into the disc space. The guide extends along alongitudinal axis from a distal to a proximal end. The guide has a firstexternal guide surface with a predetermined geometry. A drill guide isplaced against the centering guide. The drill guide is adapted toaxially guide a drill. The drill guide has an external guided surfacewhich is shaped complementary to the external guide surface of thecentering guide. The external guide surface and the guided surface aremutually nested with the guided surface sliding against the externalguide surface along a path of travel parallel to the longitudinal axisof the centering guide. The drill guide is slid toward the vertebraewith the guide surface and the guided surface maintaining movement ofthe drill guide along the desired path of travel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a prior art implant for use with themethod of the present invention;

FIG. 2 is a view of the implant of FIG. 1 with the implant rotated 90°about its axis;

FIG. 3 is a view taken along line 3--3 of FIG. 1;

FIG. 4 is a view taken along line 4--4 of FIG. 3;

FIG. 5 is a view taken along line 5--5 of FIG. 2;

FIG. 6 is a view taken along line 6--6 of FIG. 3;

FIG. 7 is a side elevation of a first embodiment of a centering guideaccording to the present invention for use in a posterior approach andwithout a lordotic distal end;

FIG. 8 is a view taken along line 8--8 of FIG. 7;

FIG. 9 is a top plan view of the centering guide of FIG. 7;

FIG. 10 is a side elevation view of a second embodiment of a centeringguide according to the present invention for use in an anterior approachand without a lordotic distal end;

FIG. 11 is a view taken along line 11--11 of FIG. 10;

FIG. 12 is a top plan view of the centering guide of FIG. 10;

FIG. 13 is a side elevation view of a third embodiment of a centeringguide according to the present invention for use in an anterior approachand with a lordotic distal end;

FIG. 14 is a view taken along line 14--14 of FIG. 13;

FIG. 15 is a top plan view of the centering guide of FIG. 13;

FIG. 16 is a side elevation view of a fourth embodiment of the centeringguide according to the present invention for use in a posterior approachand with a lordotic distal end;

FIG. 17 is a view taken along line 17--17 of FIG. 16;

FIG. 18 is a top plan view of the centering guide of FIG. 16;

FIG. 19 is a side elevation tube of a prior art drill tube for use withthe present invention;

FIG. 20 is a view taken along line 21--21 of FIG. 19;

FIG. 21 is an enlarged side elevation view of a distal end of the drilltube of FIG. 19;

FIG. 22 is a side elevation view of a prior art boring tool for use withthe present invention;

FIG. 23 is an elevation view of a proximal end of the boring tool ofFIG. 22;

FIG. 24 is an enlarged view of a boring head of the boring tool of FIG.22;

FIG. 25 is an end elevation view of a distal end of the boring head ofFIG. 24;

FIG. 26 is a side elevation view of a prior art tap for use with thepresent invention;

FIG. 27 is a view taken along line 27--27 of FIG. 26;

FIG. 28 is an enlarged sectional view of threaded cutting teeth on thetool of FIG. 26;

FIG. 29 is a side elevation view of an implant driver for use with thepresent invention;

FIG. 30 is an end view of a hub on a distal end of the tool of FIG. 29;

FIG. 31 is a view taken along line 31--31 of FIG. 29;

FIG. 32 is a side elevation view of a shaft of a tool of FIG. 29 showingan attachment collet;

FIG. 33 is a cross sectional view of FIG. 32 taken along line 33--33;

FIG. 34 is a side elevation view of a protective sleeve for use on thedrill tube of FIG. 19;

FIG. 35 is an end elevation view of the sleeve of FIG. 34;

FIG. 36 is a schematic posterior to anterior view of two vertebraeseparated by a disc space and showing a dura extending centrally along amid line between the vertebrae;

FIG. 37 is the view of FIG. 30 with a dura retracted to a left side;

FIG. 38 is the view of FIG. 37 with a centering guide of the presentinvention such as that shown in FIG. 7 inserted into the disc spacebetween the vertebrae prior to the centering guide being rotated to adistraction position;

FIG. 39 is the view of FIG. 38 with the centering guide rotated to adistraction position;

FIG. 40 is a plan view of a disc space showing the elements of FIG. 39;

FIG. 41 is a view taken along line 41--41 of FIG. 40;

FIG. 42 is the view of FIG. 39 with a drill tube of FIG. 19 insertedinto position and guided by the centering guide;

FIG. 43 is a plan view of the elements of FIG. 42 with the drill tubeshown in section;

FIG. 44 is the view of FIG. 43 following formation of a bore in the discspace and vertebrae and showing retraction of a boring tool through thedrill tube;

FIG. 45 is the view of FIG. 44 following formation of a tapped thread inthe bore of FIG. 44 and showing removal of the tapping tool through thedrill tube;

FIG. 46 is the view of FIG. 45 showing an implant inserted into thethreaded bore of FIG. 45 and showing removal of the implant driving toolthrough the drill tube;

FIG. 47 is a posterior-to-anterior view showing a dura retracted to aright side over an inserted implant and with the centering guidereversed and with a drill tube positioned against the centering guideprior to formation of a bore on the left side of the vertebra;

FIG. 48 is a plan view of the elements of FIG. 47 with the drill tubeshown in section;

FIG. 49 is an anterior-to-posterior view of two vertebrae separated by adisc space and showing a non-lordotic, anterior approach centering guideof the present invention (such as that shown in FIG. 10) and showninserted into the disc space between the vertebrae and with a drill tubebeing guided by the centering guide;

FIG. 50 is the view of FIG. 49 showing an implant inserted into a formedbore on a left side of the vertebrae and with the drill tube moved to beguided by an opposite side of the centering guide prior to formation ofa bore on the right side of the vertebra;

FIG. 51 shows a drill tube of FIG. 19 and a protective sleeve of FIG. 34guided by a posterior centering guide of FIG. 7;

FIG. 52 shows a still further embodiment of a centering guide;

FIG. 53 is a side elevation view of an alternative embodiment of a drilltube for use with the centering guide of the present invention;

FIG. 54 is a view taken along line 54--54 of FIG. 53;

FIG. 55 is the view of FIG. 53 with drill tube rotated 90° about itslongitudinal axis; and

FIG. 56 is a view taken along line 56--56 of FIG. 53.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A. Implant

Referring now to the several drawing figures in which identical elementsare numbered identically throughout, a description of the preferredembodiment of the present invention will now be provided. For purposesof illustrating the preferred embodiment, a description of the surgicalprocedure will be give with respect to an implant 10 such as that shownand described in commonly assigned U.S. Pat. No 5,489,307. It will beappreciated that the present surgical procedures and apparatus can applyto a wide variety of implants including threaded implants such as thoseshown in U.S. Pat. Nos. 5,489,307 and 5,015,247, non-cylindricalimplants such as those shown in U.S. Pat. No. 5,609,636 as well asconical implants for use in maintaining a desired lordosis. The term"implant" as used herein may also include bone implants as well asmetallic implants.

The implant 10 (FIGS. 1-6) is a hollow cylinder 12 having male,square-profile threads 14 exposed on the exterior cylindrical surface ofcylinder 12. The cylinder includes a forward interior chamber 16 and arear interior chamber 17 separated by a reinforcing rib 19. A bondslurry or bone chips may be compacted into chambers 16,17.

A first plurality of holes 18 extend radially through the cylinder walland communicate with the chambers 16,17. A second (and enlarged)plurality of holes 21 are disposed on diametrically opposed sides of theimplant 10.

A rear end 22 of the implant has a slot 24 which communicates with thechamber 17. The slot 24 allows the bone slurry or bone chips to beimpacted into the implant 10. A slot 25 is defined by rib 19. The slot25 is sized to receive a distal end of a tool (as will be more fullydescribed) to place the implant within a bore formed between opposingvertebrae. End caps (not shown) may be used with the implant. Such endcaps are shown in U.S. Pat. No. 5,489,307.

In a preferred embodiment the technique of the present invention will beperformed with a prescribed kit of tools. For the purpose ofillustrating the preferred embodiment, the tools of the kit will now bedescribed. It will be appreciated that the method of surgery can bepracticed using a wide variety of tools of different size and shapes.

Each of the tools of a kit necessary to perform the surgery as describedin this application will be separately described. The use of the toolswill become apparent with the description of the method of the inventionin Section IV.3 of this application. Unless otherwise specified, alltools are formed of stainless steel.

Since vertebrae size and disc space vary from patient-to-patient (andsince such sizes vary along the length of the spine of any givepatient), several sizes of implants 10 are anticipated. Presently,implants 10 having minor outside diameters (D_(m)) of 3 mm, 5 mm, 7 mm,9 mm, 11 mm, 13 mm, 15 mm, 17 mm, 19 mm and 21 mm with lengths (L) of 10mm, 12 mm, 14, mm 16 mm, 18 mm, 20 mm, 24 mm, 28 mm, 30 mm, 32 mm, 34mm, 38 mm, 42 mm and 44 mm, respectively, are anticipated to accommodatevarious spine locations and sizes. The major outside diameters (D_(M))of the implants 10 are 2.5 mm larger than the minor outside diametersD_(m).

Several of the tools to be described (e.g., a reaming tool 126) aresized for particular sizes of implants. Namely, the reaming tool 126must form a bore sized to receive the implant. Since ten sizes ofimplants are anticipated, ten sizes of boring tools 126 are anticipatedas will become apparent to one of ordinary skill in the art.

B. Centering Guide

1. Non-Lordotic Anterior

The present invention utilizes a novel centering guide to ensureaccurate positioning of a drill tube prior to forming a bore and placingan implant. With initial reference to FIGS. 10-12, a centering guide 100is shown for use in an anterior approach where a surgeon is approachingthe disc space from an anterior side of the patient.

The centering guide 100₁ is a rigid rod extending from a distal end 102₁to a proximal end 104₁ along a longitudinal axis X₁ --X₁. The distal end102₁ is rounded to facilitate easy insertion of the distal end 102₁ intothe disc space.

The anterior guide 100₁ has, in cross section, a major transverse axisY₁ --Y₁ with the guide being symmetrical about the axis Y₁ --Y₁ and axisX₁ --X₁. At the distal end 102₁, the guide 100₁ has a distractionportion 106₁. The distraction portion 106₁ is defined by parallel andspaced-apart side edges 108₁ which are spaced apart by a distance equalto desired distraction of the vertebrae.

The side edges 108₁ act against the end plates of the opposing vertebraeto urge the vertebrae apart. The end plates hold the centering guide100₁ with the axis X₁ --X₁ centrally positioned between the end plates.While the tool proximal end 104₁ can be moved left or right relative tothe vertebrae, the precise central positioning of the proximal end 104₁can be determined through x-ray analysis following placement of thecentering guide 100₁ such that a surgeon can be assured that thelongitudinal axis X₁ --X₁ extends perpendicular to a transverse plane ofthe vertebrae.

The distraction portion 106₁ is provided with a plurality of indicia110₁ in the form of grooves positioned at 5 millimeter increments fromthe distal end 102₁. The grooves 110₁ are detectable in x-ray films topermit a surgeon to measure the degree of insertion of the distal end102₁ into a disc space. The guide 100₁ includes a stop 109₁ on edges108₁. The stop 109₁ abuts vertebrae to prevent further insertion ofguide 100₁ beyond full insertion of portion 106₁.

Extending between the side edges 108₁ and extending the length from end102₁ to end 104₁ are left and right (or first and second) guide surfaces112₁,114₁. The guide surfaces 112₁,114₁ are concave and have a radius ofcurvature equal to a radius of curvature of a drill tube as will bedescribed. While the preferred embodiment of the present invention willbe described with reference to using a drill tube having a geometrywhich is complimentary to the guide surfaces 112₁, 114₁, it will beappreciated that the present invention could be performed without adrill tube and by using a drill, tap or other implement to facilitateinsertion of an implant where the implement has a curved geometry tomatch the radius of curvature of the guide surfaces 112₁, 114₁ in whichcase the implement is directly guided by the guide surface, rather thanbeing guided by an intermediate drill tube.

The proximal end 104₁ is provided with a hole 105₁ to permit a surgeonto place a tool (not shown) into the hole 105₁ to twist the centeringguide 100₁ to release the centering guide 100₁ if necessary. Also, anangled hole 107₁ is provided near portion 106₁ to permit insertion of arod (not shown) into hole 107₁ to permit a surgeon to force the guide100₁ to the mid-line of vertebrae. With the centering guide 100₁ of FIG.7 the end plates of the vertebrae will be distracted in parallel spacedapart relation since the side walls 108₁ are parallel at the distractionportion 106₁.

2. Non-Lordotic Posterior

FIGS. 7-9 show a centering guide 100₂ similar to that of FIGS. 10-13 butdiffering due to the fact that centering guide 100₁ of FIGS. 7-9 isintended for use in a posterior approach where a surgeon approaches thevertebrae from the posterior side of the patient. In the embodiments ofFIGS. 7-18, simple elements are numbered similarly with the addition ofsubscripts to distinguish the embodiments.,

Like the centering guide 100₁ of FIGS. 10-12, the centering guide 100₂of FIGS. 7-9 is for a non-lordotic parallel distraction appliance wherethe side edges 108₂ are spaced apart in parallel alignment at thedistraction portion 106₂. Unlike the centering guide 100₁ of FIGS.10-12, the centering guide 100₂ of FIGS. 7-9 is not symmetrical aboutits major transverse axis Y₂ --Y₂ (although it is symmetrical about axisX₂ --X₂. Instead, the centering guide 100₂ of FIGS. 7-9 includes only afirst concave guiding surface 112₂ extending on one side of thecentering guide 100₂. The opposite surface 114₂ is a convex surface topresent a smooth surface opposing a dura following insertion of thecentering guide 100₂ as will be described.

3. Lordotic Posterior

The centering guides 100₁,100₂ of FIGS. 7-12 both show distractionportions 106₁,106₂ having distracting edges 108₁,108₂ which are paralleland spaced apart. From time to time, it may be desirable to ensure thatend plates of opposing vertebrae are retained at a desired degree oflordosis (i.e., with a non-parallel angle between end plates of theopposing vertebrae).

FIGS. 16-18 show a centering guide 100₃ for a posterior approach andhaving a lordotic distraction portion 106₃. The distraction portion 106₃has side edges 108₃ placed at an angle, A, equal to the desired degreeof lordosis. In all other respects, the centering guide 100₃ of FIGS.16-18 is identical to that of FIGS. 7-9.

4. Lordotic Anterior

FIGS. 13-15 show a lordotic centering guide 100₄ for use in an anteriorapproach. The distractor end 106₄ of the tool 100₄ has distracting sideedges 108₄ set at a lordotic angle, A', equal to but reverse that of theembodiment of FIGS. 16-18. In all other respects, the centering guide100₄ of FIGS. 13-15 is identical to that of FIGS. 10-12.

5. Laparoscopic

Laparoscopic versions of both the lordotic and non-lordotic centeringguides can also be provided. Although not shown in the drawings, suchlaparoscopic centering guides would have a shorter length than thenon-laparoscopic centering guides shown in the drawings. For example, anon-lordotic, laparoscopic anterior centering guide would be identicalto that of guide 100₁ (FIG. 10) but have its axial length detachable sothat the terminal end 104₁ is spaced from the distal tip 102₁ by about 3inches. After insertion of the portion 106₁ into the disc space,approximately 1.5 inches of the guide surfaces 112₁, 144₁ would protrudebeyond the vertebrae and provide a guide surface for directing alaparoscopic drill tube. The design would also permit the maintenance ofinsufflation.

C. Drill Tube

A drill tube 92 (FIGS. 20-22) is provided in the form of a hollowcylindrical tube 94. The distal end 96 of the tube 94 is provided withaxially projecting teeth 98. The proximal end 99 of the tube 94 isflared outwardly. As will be apparent, ten sizes of tube 92 are requiredwith inside diameters D_(DT) to slip in close tolerance over ten sizesof implants 10 (i.e., D_(DT) is 0.5 mm larger than D_(M)).

The teeth 98 each have a length, T_(L), of preferably 3 mm. The valleys97 are flat to provide stop surfaces to hit bone as teeth 98 are forcedinto vertebrae. This helps prevent the drill tube 92 from being forcedtoo far into bone. The drill tube 92 is identical to that shown in U.S.Pat. No. 5,489,307.

An alternative embodiment of a drill tube 192 is illustrated in FIGS.53-56. The drill tube is a hollow cylindrical tube 194 with an outsidediameter having a radius of curvature to match the radius of curvatureof the guide surfaces 112₁, 114₁. The distal end 196 of the tube 194includes diametrically opposed and axially projecting sharpened teeth198 for penetration into vertebrae. Diametrically opposed and axiallyextending retraction paddles 199 are provided ninety degrees offset fromthe teeth 198 (with reference to the longitudinal axis (X'_(D)--X'_(D)). The paddles 199 have a width (W in FIG. 54) equal to thedesired distraction of the vertebrae. The proximal end 197 of the tube194 is a handle to be gripped by a surgeon. The tube 194 has a lengthL_(D) measured from the base of the teeth 198 and retraction paddles 199to the base of the handle 197. The length L_(D) is equal to the lengthof a centering guide (such as the length of guide 100₁ of FIG. 10)between the proximal end 104₁ and the insertion portion 106₁. Therefore,when the insertion portion 106₁ is fully inserted into the disc space,the end 104₁ buts against the handle 197 when the teeth 198 are forcedinto the vertebrae.

D. Vertebral Reamer

A vertebral reamer 126 (or boring tool) (FIGS. 22 through 25), isprovided for forming a bore. The reamer 126 is such as that shown inU.S. Pat. No. 5,489,307. The reamer 126 includes a shaft 128. A distalend of the shaft is provided with a reamer end 130 having side and endcutting blades 131. A proximal end of the shaft is provided with anoutwardly flared hub 132. Extending from hub 132 is an axial shaft 134.For ten sizes of implants 10, ten sizes of reamers 126 are required withthe kit. The outside diameter D_(R) of reamer 126 equals the minoroutside diameter D_(m) of implants 10. The diameter D_(RG) of the guidehub 133 equals the inner diameter of the drill tube D_(DT).

E. Bone Tap

In the event a threaded implant is utilized (as is the case in thepreferred embodiment of the present invention), the bores for theimplants are partially pre-threaded. To pre-thread, a bone tap 142(FIGS. 26-28) is provided, having a shaft 144. The top 142 is such asthat shown in U.S. Pat. No. 5,489,307. At the distal end of the shaft144 is a tapping head 146 having tapping threads 148. Near the proximalend of the shaft 144 is an enlarged diameter portion 156 having anoutwardly flared flange 158. A handle 160 is secured to an enlargedportion 156. The shaft 144 is also enlarged at portion 162 adjacenttapping head 146. The enlarged portion 156 is sized with diameter D₈ tobe received, in close tolerance, within the drill tube 92 such that thetube 92 will guide the tap 142 as will be more fully described.

Since ten sizes of implants 10 are intended to be utilized, ten sizes ofbone taps 142 are required. Diameter D_(T) is equal to the major outsidediameter D_(M) of implant 10. The head 146 has a minor outside diameterD_(t) (i.e., the diameter without threads 148) equal to the minoroutside diameter D_(m) of the implants 10.

F. Implant Driver

To place implant 10, an implant driver 164 (FIGS. 29 through 33) isprovided. The driver 164 is such as that shown in U.S. Pat. No.5,487,307. A driver is also shown in U.S. Pat. No. 5,609,636. The driver164 includes a shaft 166 having a reduced diameter distal portion 166a.A distal end of the shaft 166 is provided with a hub 168 sized to bereceived within slot 24 of the implant 10 to urge the implant 10 torotate as the implant driver 164 is rotated. The implant driver 164includes a stepped enlarged portion 170 including a first diameterportion 172, a second diameter portion 174 and a third diameter portion176 to accommodate the different diameters of drill tubes 92. A handle178 is secured to the shaft 164. Grooves 180,180a are formed on theshafts 166,166a and extend along their axial lengths. The grooves 180provide a means for a surgeon to sight the alignment of the implant.

FIGS. 32-33 show the implant driver 164 with a collet 171. The collet171 has a cylindrical, knurled body 173 slidably carried on shaft 166a.A pin 175 extending from body 173 into groove 180a permits collet 171 toslide on shaft 166 but not rotate. Four prongs 177 extend axially frombody 173 toward hub 168.

In use, shaft 166 is passed through end opening 24 of implant 10. Hub168 is received within slot 25. The prongs 177 are forced by a surgeonpushing on body 171 for the prongs 177 to be urged between opposingsurfaces of the implant 10 and shaft 166a to thereby securely capturethe implant 10 on driver 164. As a result, the implant 10 cannotinadvertently fall off. (For ease of illustration, the Figures showingthe method of the invention, e.a., FIG. 46, does not show use of collet171).

G. Drill Tube Sheath

Drill tube 92 is passed through a patient's body to an implant site. Toavoid risk of teeth 98 damaging vessels, nerves or organs, a drill tubesheath 300 is provided (FIGS. 34,35). The sheath 300 is such as thatshown in U.S. Pat. No. 5,489,307. The sheath 300 is a hollow tube withinside diameter D_(S) slightly smaller than the outside diameter ofdrill tube 92 (accordingly, ten sizes of sheath 300 are required). Thesheath 300 has an axial slit 301 extending its entire length. The sheath300 has a blunt distal end 302 and a flared proximal end 304.

The sheath is slipped onto the drill tube 92 with end 302 extendingbeyond the teeth 98. As the drill tube 92 is passed to an implant sitethe blunt end 302 covers the teeth and prevents the unwanted cutting ofvessels, nerves or organs. When pressed against vertebrae, the end 302abuts the vertebrae. With continued advancement of the tube 92 towardthe vertebrae, the sheath 300 slides on the tube 92 until teeth 98 abutthe vertebrae.

In the method of the invention, sheath 300 remains in place wheneverdrill tube 92 are used. However, for ease of illustration, sheath 300 isnot shown in FIGS. 42-50.

H. Posterior Technique

The present invention will first be described with reference to use in aposterior approach. In a posterior approach, a surgeon seeks access tothe spine through the back of the patient. Another alternative approachis the lateral approach, where the patient is on his side and a singlecage is inserted across the disk space. An alternative approach is ananterior approach where the surgeon seeks access to the spine throughthe abdomen of a patient. The approaches can be done through opensurgery or through laparoscopic surgery.

While a posterior approach will be described in detail, it will beappreciated that the present invention can be used in an anterior orlateral approach for both laparoscopic or non-laparoscopic procedures.

With initial reference to FIG. 36, once a surgeon has identified twovertebrae 200,200' which are to be fused together, the surgeonidentifies an implant 10 of desired size and the surgeon determines thedesired amount of distraction of the disc space 202 to be requiredbefore placement of the implant 10. In selecting the implant size, thesurgeon should ensure that the device will remain within the lateralborders of the intervertebral disc space 202 while also penetrating atleast 3 mm into the vertebral bodies 200,200' cephalad and caudal to thedisc.

In the posterior technique, a patient is placed on the operating tablein either a prone or kneeling-sitting position. At the discretion of thesurgeon, the spine is flexed slightly. Anesthesia is administered.

Exposure of the intervertebral disc is obtained through any suitabletechnique well-known in the art. The facet of the vertebrae is removedin as limited amount as possible to permit insertion of the instrumentsand the implants. Preferably, bone dissected from the lamina, facets andspinous process are preserved for later use as bone graft.

FIG. 36 shows two vertebrae 200,200' separated by a disc space 202. Forease of illustration, disc material is not shown in space 202 having anundistracted thickness T_(R). In the posterior P to anterior A view, adura 204 extends between the vertebrae 200,200' and is centrallypositioned along a medial line, M, between the vertebrae 200,200'. Theline M separates the disc space 202 and vertebrae 200,200' into a leftside L and right side R corresponding to the patient's left and rightsides.

As shown in FIG. 37, the dura 204 is first retracted to the left throughany suitable means to expose the disc space 202 and vertebrae 200,200'at the medial line, M. A distal end 102₂ of the centering guide 100₂ ofFIGS. 7-9 is inserted into the disc space 202 in the manner illustratedin FIG. 38 with the distracting side edges 108₂ opposing and in linewith the disc space 202.

After initial insertion of the distal end 102₂ into the disc space, thecentering tool 100₂ is rotated 90° to the position shown in FIG. 39 suchthat the side edges 108₂ of the distraction portion 106₂ oppose anddistract the vertebrae and the convex surface 114₂ is opposing the dura204 to prevent damage to the dura 204. The vertebrae 200,200' are nowdistracted to a spacing of T_(D) equal to the distance between sideedges 108₂.

The distraction portion 106₂ of the guide 100₂ is forced into the discspace 202 at the mid line M of the disc space 202. The size (i.e, thespacing between the side edges 108₂) of the centering guide 100₂ isselected to distract the annulus fibrosus without causing damage to thesurrounding vertebral bone, annular fibers or spinal nerves.Accordingly, it is recommended that a surgeon initially insert arelatively narrow distal end centering guide (e.g., 6 millimeters)followed by successively larger guides until the annulus is distractedto the surgeon's satisfaction.

Once the correct maximum size distraction portion 106₂ has been chosen,it is left in place. The disc space 202 has now been stretched so that aparallel distraction of the end plates 201,201' of the vertebrae200,200' has occurred on both the left and right sides of the vertebrae.The distraction portion 106₂ is fully inserted such that the indicia110₂ are flush or slightly recessed within the disc space.

Following placement of the distracting centering guide 100₂, the drilltube 92 is placed against the centering guide 100₂. Since the guidingsurface 112₂ of the centering guide 100₂ is concave with a radius ofcurvature matching the outer radius of curvature of the drill tube 92,the drill tube 92 can be slid along the length of the guide 100₂ intoprecise position with the axis X_(D) --X_(D) of the drill tube 92centrally positioned between the end plates 201,201' of the vertebrae200,200'.

In a preferred embodiment, the drill tube 92 will be surrounded by asliding protective sleeve 300 such as that. shown in FIGS. 34-35 anddescribed fully in U.S. Pat. No. 5,489,307. The thin wall of the drillsleeve 300 has substantially the same radius of curvature as the drilltube 92 and does not materially affect the positioning. At most, theaddition of the protective sleeve 300 increases the spacing of the axisX_(D) --X_(D) of the drill tube 92 from the axis X₂ --X₂ of the guide100₂ (FIG. 51) but does not alter the central positioning of the axisX_(D) --X_(D) of the drill tube 92 between the end plates 201,201'. Forease of illustration, the drill sleeve protective sleeve is not shown inFIGS. 42-50.

With the drill tube 92 in place, the preparation of the implant bore 206is completed by inserting the reamer 126 into the drill tube 92 (FIG.44). The reamer 126 is rotated with any suitable driver (such as driver136 shown in U.S. Pat. No. 5,489,307).

Since the drill tube 92 is centrally placed with the axis X_(D) --X_(D)of the drill tube 92 centrally positioned between the end plates201,201', the reamer 126 will bore into the disc space 202 and boreequally into and through the end plates 201,201' of the opposingvertebrae. The reamer 126 is selected to form a bore 206 having adiameter D_(m) equal to the minor outside diameter of the implant 10 (inthe case of a cylindrical implant such as that shown in FIGS. 1-6).

For use with a threaded implant 10 such as that shown in FIGS. 1-6, abone tap 142 is passed through the drill tube 92 and rotated to at leastpartially pretap the bore (FIG. 45). The tap is then removed to expose atapped bore 207 with the drill tube 92 remaining in place. The implant10 may then be packed with a bone graft material. The graft may beautograft obtained previously from the iliac crest or some other graftmaterial (e.g., allograft or artificial bone). The implant 10 isattached to the implant driver 164 by placing the hub 168 within theslot 25 and securing the implant 10 with the collet 171. The implant 10is then passed through the drill tube 92. The implant 10 is threadedinto the bore 207 with the implant driver 164 by the surgeon rotatingthe driver 164 and advancing it into the drill tube 92. As disclosed inU.S. Pat. No. 5,489,307, it is desirable that the larger holes of theimplant are oriented in a superior-inferior direction (i.e., the largerholes are facing the vertebrae 200,200').

After the implant 10 is fully in place, the implant driver 164 isremoved through the drill tube 92 (FIG. 47). The drill tube 92 is thenremoved. The dura 204 is retracted slightly and the centering guide 100is then removed. The dura 204 is then retracted to the opposite side andthe centering guide 100₂ is repositioned with the disc space 204 butrotated 180° relative to FIG. 39 so that the rounded side 114₂ is facingboth the dura 204 and the previously placed implant 10 and the guidesurface 112₂ is facing the opposite side of the disc space 202. Theprocedure can then be repeated by placing the drill tube 92 against thevertebrae with the drill tube 92 aligned by the guide 100₂ as previouslydescribed (FIG. 47).

I. Anterior Approach

The foregoing discussion illustrates the use and method of an apparatusof the invention in a posterior approach. It will be noted that forplacing two implants 10, the centering guide 100₂ is removed andreinserted into the disc space 202 to reorient the guiding surface 112₂.

When performing an anterior approach, the surgeon uses the anteriorguide 100,100₄ which has concave guiding surfaces 112,114 on oppositesides of the centering guide 100. With such structure, the anteriorcentering guide 100 is placed at the mid line M and a drill tube 92 isguided by a first 112 of the guiding surfaces 112,114 so that a firstbore can be formed, tapped and an implant 10 inserted through the drilltube (FIG. 50). After the implant 10 is inserted, the centering guide100 remains in place but the drill tube 92 is moved to the opposite sideand guided into position by the second guiding surface 114 (FIG. 51).With the drill tube 92 in position on the second side, a bore 206 isthen formed by passing the reamer and tap through the drill tube and asecond implant is inserted through the drill tube.

J. Lateral Approach

The present invention is particularly suited for a lateral approachwhere an elongated single implant is to be placed in the inner vertebralspace. The present invention requires smaller access space to the discspace which is of particular advantage in a lateral approach where thereis substantial anatomic structure limiting access to the disc space in alateral approach at certain vertebrae locations.

K. Additional Embodiments

In the foregoing description, the guide surface has been shown as aconcave surface 112 having the same radius of curvature of the guidedsurface of the cylindrical drill tube. It will be appreciated that whilea circular arc of a guide surface corresponding to a radius of curvatureof a cylindrical drill tube is preferred, a plurality of complementarygeometries could be used for the guide surface and the guiding surface.

In the present invention, if the surgeon were to place the drill tube 92such that the axis X_(D) --X_(D) of the drill tube 92 is not parallel tothe longitudinal axis X₂ --X₂ of the centering guide 100₂, suchmisalignment could be detected at the proximal end 104₂ of the guide100₂ and be indicated by a spacing between the centering guide 100₂ andthe drill tube 92. An alternative embodiment would be to provide aguiding surface on the centering guide which locks with a guided surfaceon the drill tube such that non-parallel alignment of the axis of thedrill tube and the centering guide is not possible. For example, theguide surface 112' on the centering guide 100' could be dovetail groovedand the guided surface on the drill tube 92' could be a complementaryshaped dovetail rail 93' which slides within the dovetail groove 112'.Such a modification would preclude non-parallel alignment of the axisX_(D) '--X_(D) ' of the drill tube 92' and the longitudinal axis X'--X'of the centering guide 100'. However, such a modification would requireaccurate alignment of the drill tube 92', whereas in the preferredembodiment previously disclosed, the drill tube 92 may be rotated aboutits axis X_(D) --X_(D).

From the foregoing detailed description of the present invention it hasbeen shown how the objects of the invention have been obtained in apreferred manner. However, modifications and equivalence of thedisclosed concepts such as those which would occur to one of ordinaryskill in the art are intended to be included within the scope of thepresent invention.

What is claimed is:
 1. A surgical method for implanting a spinal fusionimplant into a disc space separating a first vertebra and a secondvertebra, said method comprising:inserting a distal end of a rigidcentering guide into said disc space in a first orientation with saidrigid centering guide extending along a longitudinal axis from saiddistal end to a proximal end exterior of said disc space and with saidguide having a first external guide surface of predetermined geometry;rotating said rigid centering guide around said longitudinal axis to asecond orientation to distract said first and second vertebra; placingan implement against said centering guide with said implement having anexternal guided surface shaped complementary to said first externalguide surface for said first external guide surface and said guidedsurface to be nested with said guided surface sliding against said firstguide surface along a path of travel parallel to said longitudinal axis;sliding said implement toward said vertebrae with said first guidesurface and said guided surface maintaining movement of said implementalong said path of travel.
 2. A method according to claim 1 comprisinginserting said distal end from an anterior approach and selecting saiddistal end to have opposite side edges defining an angle approximate toa desired angle of lordosis between said disc space.
 3. A methodaccording to claim 1 comprising inserting said distal end from aposterior approach and selecting said distal end to have opposite sideedges defining an angle approximate to a desired angle of lordosisbetween said disc space, said distal end inserted by first insertingsaid distal end into said disc space in said first orientation with saidside edges rotated to oppose said disc space and subsequently rotatingsaid distal end within said disc space to said second orientation forsaid side edges to oppose and distract said vertebra.
 4. A methodaccording to claim 1 wherein said guide includes said first externalguide surface and a second external guide surface, said first and secondexternal guide surfaces positioned on opposite sides of saidlongitudinal axis with each of said first and second external guidesurfaces shaped complementary to said external guided surface of saidimplement for a selected one of said first and second external guidesurfaces to nest with said guided surface for said guided surface toslide against said selected one along said path of travel, and whereinsaid implement is a drill guide adapted to axially guide a drill, saidmethod further comprising:sliding said drill guide toward said vertebraeagainst said first guide surface; inserting a drill through said drillguide and boring a first bore; inserting an implant into said firstbore; sliding a drill guide toward said vertebrae against said secondguide surface; inserting a drill through said drill guide and boring asecond bore; and inserting an implant into said second bore.
 5. A methodaccording to claim 1 wherein said guide includes an external secondsurface on a side of said longitudinal axis opposite said first guidesurface, said second surface being convex to present a smooth surfaceopposing a dura, said method including:retracting a dura beforeinserting said distal end into said disc space; and placing said distalend into said disc space with said second surface opposing said dura. 6.A surgical method for distracting a first vertebra and a second vertebraadjacent a disc space, said method comprising:inserting a distal end ofa rigid centering guide into said disc space in a first orientation withsaid rigid centering guide extending along a longitudinal axis from saiddistal end to a proximal end exterior of said disc space and with saidguide having a first external guide surface, said distal end of saidrigid centering guide mounted to said proximal end of said centeringguide and configured such that said distal end of said rigid centeringguide is inserted into said disc space in said first orientation andupon rotation of said rigid centering guide around said longitudinalaxis to a second orientation distracts said first and second vertebrae;rotating said rigid centering guide around said longitudinal axis fromsaid first orientation to said second orientation to distract said firstand second vertebrae.
 7. The method according to claim 6 furthercomprising a step of:placing an implement against said centering guidewith said implement having an external guided surface shapedcomplementary to said first external guide surface for said firstexternal guide surface and said guided surface to be nested with saidguided surface sliding against said first guide surface along a path oftravel parallel to said longitudinal axis; sliding said implement towardsaid vertebrae with said first guide surface and said guided surfacemaintaining movement of said implement along said path of travel.
 8. Amethod according to claim 6 comprising inserting said distal end from ananterior approach and selecting said distal end to have opposite sideedges defining an angle approximate to a desired angle of lordosisbetween said disc space.
 9. A method according to claim 6 comprisinginserting said distal end from a posterior approach.
 10. A methodaccording to claim 6 comprising inserting said distal end from aposterior approach and selecting said distal end to have opposite sideedges defining an angle approximate to a desired angle of lordosisbetween said disc space, said distal end inserted by first insertingsaid distal end into said disc space in said first orientation with saidside edges rotated to oppose said disc space and subsequently rotatingsaid distal end within said disc space to said second orientation forsaid side edges to oppose and distract said vertebra.
 11. A methodaccording to claim 6 wherein said guide includes said first externalguide surface and a second external guide surface, said first and secondexternal guide surfaces positioned on opposite sides of saidlongitudinal axis with each of said first and second external guidesurfaces shaped complementary to said external guided surface of saidimplement for a selected one of said first and second external guidesurfaces to nest with said guided surface for said guided surface toslide against said selected one along said path of travel, and whereinsaid implement is a drill guide adapted to axially guide a drill, saidmethod further comprising:sliding said drill guide toward said vertebraeagainst said first guide surface; inserting a drill through said drillguide and boring a first bore; inserting an implant into said firstbore; sliding a drill guide toward said vertebrae against said secondguide surface; inserting a drill through said drill guide and boring asecond bore; and inserting an implant into said second bore.
 12. Amethod according to claim 6 wherein said guide includes an externalsecond surface on a side of said longitudinal axis opposite said firstguide surface, said second surface being convex to present a smoothsurface opposing a dura, said method including:retracting a dura beforeinserting said distal end into said disc space; and placing said distalend into said disc space with said second surface opposing said dura.